It looks like an acpi problem. Initializing the nouveau driver
at that point is coincidental. Ie, acpi is waiting for some probe
to return information, the kernel pauses it to handle a notification
from the nouveau driver, and somehow acpi never restarts
(missed the probe return, still waiting when the nouveau
driver finishes its initialization). Missing lock?

There is a linux-acpi bugzilla and mailing list. You might search either for
mention of nouveau to see if anyone else has reported a similar bug.
You can also search for mention of your mb, mb chipset, BIOS version,
etc, in the context of acpi.